The present invention generally relates to contact type image sensors, and more particularly to a contact type image sensor which generates uniform outputs from all of photoelectric conversion elements thereof.
Generally, a contact type image sensor comprises a transparent substrate, a lower stop layer formed on the transparent substrate and having windows, a transparent insulator layer formed on the lower stop layer, a lower electrode formed on the transparent insulator layer and having windows, a photoelectric conversion part formed on the lower electrode, and an upper electrode which connects to a transparent electrode via through holes of the transparent insulator layer. The photoelectric conversion part comprises an amorphous silicon layer, photoelectric conversion elements and the transparent electrode. The lower electrode is not limited to an optically non-transparent conductive thin film having the windows. For example, it is possible to form on the transparent insulator layer another stop layer having the windows and form an optically transparent conductive thin film (lower electrode) on this other stop layer.
In order to obtain uniform outputs from the photoelectric conversion elements and to improve a modulation transfer function (MTF) of the contact type image sensor, there are usually provided a number of windows dependent on the number of photoelectric conversion elements (reading elements). But conventionally, there are problems in that the outputs obtained from the photoelectric conversion elements of such a contact type image sensor are not constant and a signal-to-noise (S/N) ratio of the contact type image sensor is poor.